yum安装编译内核
升级前环境：

[root@localhost ~]# uname -a
Linux localhost.localdomain 3.10.0-514.el7.x86_64 #1 SMP Tue Nov 22 16:42:41 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
[root@localhost ~]# cat /etc/*release
CentOS release 6.8 (Final)
LSB_VERSION=base-4.0-amd64:base-4.0-noarch:core-4.0-amd64:core-4.0-noarch:graphics-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch
CentOS release 6.8 (Final)
CentOS release 6.8 (Final)
[root@localhost ~]#

导入public key
这步必须要执行的，rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org

[root@localhost ~]# rpm --import https://www.elrepo.org/RPM-GPG-KEY-elrepo.org
[root@localhost ~]#

安装ELRepo到CentOS
可以去http://elrepo.org/tiki/tiki-index.PHP 选择要安装的ELRepo

若只想升级至当前的最新稳定内核，只需要执行下面命令
[root@localhost ~]# rpm -Uvh http://www.elrepo.org/elrepo-release-6-8.el6.elrepo.noarch.rpm

[root@localhost ~]# rpm -Uvh http://www.elrepo.org/elrepo-release-6-8.el6.elrepo.noarch.rpm
Retrieving http://www.elrepo.org/elrepo-release-6-8.el6.elrepo.noarch.rpm
curl: (22) The requested URL returned error: 404 Not Found
error: skipping http://www.elrepo.org/elrepo-release-6-8.el6.elrepo.noarch.rpm - transfer Failed
[root@localhost ~]# rz
-bash: rz: command not found
[root@localhost ~]# rpm -Uvh elrepo-release-6-8.el6.elrepo.noarch.rpm
Preparing...                ########################################### [100%]
   1:elrepo-release         ########################################### [100%]
[root@localhost ~]#

如果失败可以先下载下来再更新

[root@localhost ~]# yum --enablerepo=elrepo-kernel install kernel-lt -y 安装 kernel-lt
[root@localhost ~]# yum --enablerepo=elrepo-kernel install -y kernel-ml 或者 安装kernel-ml（ml=mainline）

[root@localhost ~]# yum --enablerepo=elrepo-kernel install kernel-lt -y 
Warning: RPMDB altered outside of yum.
  Installing : kernel-lt-4.4.111-1.el6.elrepo.x86_64                                                                                                             1/1 
  Verifying  : kernel-lt-4.4.111-1.el6.elrepo.x86_64                                                                                                             1/1 

Installed:
  kernel-lt.x86_64 0:4.4.111-1.el6.elrepo                                                                                                                            

Complete!
[root@localhost ~]#

编辑grub.conf文件，修改Grub引导顺序

[root@localhost ~]# vim /etc/grub.conf
#boot=/dev/sda
default=0
#default=1
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz

一般新安装的内核在第一个位置，所以设置default=0，表示启动新内核，修改后重启系统

[root@localhost ~]# uname -a
Linux localhost.localdomain 4.4.111-1.el6.elrepo.x86_64 #1 SMP Wed Jan 10 14:56:14 EST 2018 x86_64 x86_64 x86_64 GNU/Linux
[root@localhost ~]#

若只想升级只指定的内核，或者由于不能访问到源地址，也可以用以下方法。
在以下两个网址中找到想要的内核:
1、http://elrepo.reloumirrors.net/kernel/el7/x86_64/RPMS/ //官方源
2、http://hkg.mirror.rackspace.com/elrepo/kernel/el7/x86_64/RPMS/ //香港镜像，最新版本会比官网延迟1、2天

上图中显示当前最新版本是http://elrepo.reloumirrors.net/kernel/el7/x86_64/RPMS/kernel-ml-devel-4.14.13-1.el7.elrepo.x86_64.rpm （ MainLine = ml ），
yum install -y http://elrepo.reloumirrors.net/kernel/el7/x86_64/RPMS/kernel-ml-devel-4.14.13-1.el7.elrepo.x86_64.rpm